The invention relates to a method of filtering radioactive offgases and regenerating the filters at temperatures in excess of 500.degree. C., in which, for cleaning the filters, the filtered substances are removed from the filters by removing the contaminated layer of filter material in the direction opposed to the direction of impingement of the offgases onto the filters.
Previously, filter candles made of porous ceramic materials or metal fiber fleece were used to retain the aerosol fraction of radioactive offgases with temperatures in excess of 500.degree. C. at the point at which they were to be cleaned. However, especially in the solidification of high level waste in glass or ceramic matrices or glass-like or ceramic-like matrices, this technique did not prove to work satisfactorily in long time operation, but rather became the weak point in any facility requiring a filter system of this kind. As experiments went on, it became increasingly more difficult to blow back the filters until, finally, they had to be replaced.
In large scale drying steps, with correspondingly large offgas volumes of water vapor and non-condensable gases of the type needed in more recent designs of plants for the solidification of aqueous high level waste concentrates, there is also increased aerosol formation even in drip drying of the liquid.